SEPARATION, PURIFICATION AND RECOVERY METHOD OF SF6, HFCs AND PFCs

ABSTRACT

A separation, purification and recovery method of SF 6 , HFCs or PFCs is disclosed, which comprises a step for forming a gas hydrate including components in addition to SF 6 , HFCs or PFCs. It is possible to separate and recover fluoro-gas at a much lower cost as compared to a conventional method for thereby obtaining an economical effect and preventing an emission of SF 6 , HFCs or PFCs which corresponds to Non-CO 2  having a higher earth warming index, which leads to preventing an earth warming phenomenon. So, the present invention might be widely applied.

TECHNICAL FIELD

The present invention relates to a separation, purification and recovery method of SF₆, HFCs or PFCs, and in particular to a separation, purification and recovery method of SF₆, HFCs or PFCs through a solid/liquid separation after an intensive concentration in a gas hydrate state by reacting a gas such as SF₆, HFCs or PFCs with water.

BACKGROUND ART

SF₆, HFCs or PFCs is known to have a higher earth warming index and a longer life span and is designated as six representative earth warming gases along with CO₂, CH₄ and N₂O. In particular, SF₆ has the highest earth warming impact level among six representative earth warming gases and has 23,900 times higher earth warming index as compared to CO₂ which is one of representative earth warming gases. So, SF₆ is the worst environment pollutant.

In addition, all countries including advanced countries as well as developing countries are included in the group for greenhouse gas emission cut countries after 2013 in accordance with the weather protocol which was adapted in the 13^(th) UNFCCC(United Nations Framework Convention on Climate Change) on Dec. 15, 2007. Korea will be a member of the duty reduction countries in 2013, so a greenhouse gas reduction should be implemented. It is urgent that an economic and efficient measure for a separation and recovery of SF₆, which causes a serious greenhouse gas effect, should be sought and set.

In a conventional method for a separation, purification and recovery of all kinds of gases including fluoro-gases of SF₆, HFCs and PFCs, all mixed gases are liquified and distilled depending on their boiling points and are used.

Since the liquification temperatures of gases are very low, there are a lot of difficulties for liquification, and a lot of energy is needed. So, a low energy consumption process is being developed in a process of separating a specific component from multi-component mixed gases.

For example, the US patent gazette 2002/0062734 discloses a method of separating nitrogen and SF₆ using a membrane separation method.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide a new and efficient separation, purification and recovery method of SF₆, HFCs or PFCs.

To achieve the above objects, there is provided a separation, purification and recovery method of fluoro-gases such as SF₆, HFCs or PFCs for thereby separating and recovering after fluoro-gases are intensively concentrated in a gas hydrate state.

EFFECTS

Since fluoro-gases can be concentrated 100 times intensively by using a hydrate formation method and then can be separated in a gas hydrate state, it is possible to significantly reduce the consumption of energy as compared to a conventional representative liquification method for thereby more effectively coping with an international environment regulation by reducing the emission of Non-CO₂ greenhouse gas of SF₆, HFCs or PFCs which has about 24,000 times higher earth warming index as compared to CO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a hydrate phase of SF₆ gas according to the present invention.

FIG. 2 is a view of a mechanism of a nano-size particle promoter according to the present invention.

FIG. 3 is a SF₆ 50%(N₂ Balance) hydrate formation ratio graph according to the present invention.

FIG. 4 is an analysis graph using a GC of a dissociation gas based on a dissociation of hydrate formed by using SF₆ 50%(N₂ Balance) according to the present invention.

FIG. 5 is a graph of a result of a SF₆ hydrate kinetic experiment based on an addition concentration by using Linear Alkyl Benzene Sulfonate, LABS, Aldrich as gas hydrate promoter according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

The construction and embodiments of the present invention will be described with reference to the accompanying drawings.

Gas hydrate has a cavity in a 3D lattice structure formed as water molecular and hydrogen are coupled under a high pressure and low temperature condition. Gases are physically caught in the above cavity. The most known gas hydrate is methane hydrate. In case that hydrate is made by reacting methane with water, a relatively higher atmosphere of 20 bar is required at 4° C.

However, in case of fluoro-gas to be separated according to the present invention, as shown in FIG. 1, the fluoro-gas can be easily crystallized under about 2.4 bar at 4° C and under 3.5 bar at a room temperature. The inventor of the present invention has separated and recovered the fluoro-gas in a hydrate state using the above condition.

For example, in case that a gas mixture including nitrogen and SF₆ at a molecular ratio of 7:3 is separated using a liquification method, a lot of energy is needed in a compression process. However, in case that it is separated using a hydrate formation principle, energy might be consumed at a cost of a heating control during a hydrate generation process, so cost might be down above 20% as compared to a liquification method, which leads to a very economical consumption.

In the present invention, an agitation process is performed using an impeller as a gas/liquid contact process so as to increase a contacting area between gas molecular and water molecular which are used in a reaction. In addition, micro liquid drops are sprayed using a micro liquid drop generation device, and hydrate is generated. As the size of each liquid drop decreases, a contacting area between water molecular and gas molecular increases with respect to a unit volume of gas, which leads to an innovative generation efficiency.

In addition, it is possible to more decrease an energy cost needed for a fluoro-gas separation recovery process with the helps of a gas hydrate formation speed promotion(Kinetic promotion) and a hydrate formation condition release(Thermodynamic promotion) by adding a nano size material which functions as a promoter during a hydrate formation process.

A nano size inorganic material stably dispersed in a host water induces and increases a concentration of gas in water by providing a gas adsorption site to a guest. In addition, the nano size inorganic material provides an environment that hydrates can concurrently grow in a cluster shape by providing a concurrent and multiple nucleus formation site due to a large specific surface area. Since a promoter having a higher thermal conductivity is able to effectively disperse latent heat during a formation of hydrate, it is expected to help a crystal growth of hydrate.

As an anion or cation surface active agent having a promoter function, there are LABS(linear alkyl benzene sulfonate), SDS(sodium dodecyl sulfate), TMA(Tri Methyl Amine), THF(Tetrahydrofuran), TFT(Trifluorotoluene), CuCl, 2,2-bipyridine, 1,1,2-trichlorotrifluoroethane, ether, ethanol, chloroform, CH₂Cl₂(Methylene dichloride), TEA(trietylamine), MPEO(methoxy polyethylene glycol), TBABB(tetrabutyl ammonium bibenzoate), MTSDA(methyl trimethyl silyl dimethyl ketene acetal), BBB(2-bromoisobutyryl bromide), DMAP(4-(Dimethylamino)pyridine, 1H,1H-FOMA(1H,1H-perfluorooctyl methacrylate), 1H,1H,2H,2H-FOMA(1H,1H,2H,2H-perfluorooctyl methacrylate), PEPECOOH(perfluoropolyether carboxylic acid) and TTIP(Titanium (IV) triisopropoxide).

The above research and concept are first in the world. Namely, it is possible to achieve a kinetic promoter function, which promotes a hydrate formation, in combination with a guest concentration increase, a concurrent growth and an effective dispersion function of latent heat.

As shown in FIG. 2, when a nano size promoter is used, a high intensive gas hydrate can be fast formed. Since a nano size particle has a large specific surface area, it can provide an adsorption site, and the density of a guest increases. Since it can be concurrently grown with the help of a nucleus formation site, a high intensive gas hydrate can be fast formed. A nano size particle such as a nano size carbon particle has a high heat conductivity, so it can disperse latent heat, which helps a crystal growth.

The present invention might be well understood along with the following embodiments, and it is obvious that the present invention might not be limited by means of the following embodiments and experiment examples.

Embodiment 1 Separation, Purification and Recovery Ratio Experiment of SF₆ and Mixed Gas

Pure water(HPLC grade, 99.999%) of 125 ml is injected into a reactor, and the interior of the reactor is purged a few times by using a SF₆ 50%(N₂ Balance) gas. The hydrate is formed at a pressure of 7.8 bar, a temperature of 276K, and an agitating speed of 500 rpm. The reactor is substantially cooled to a low temperature after the hydrate formation reaction is completed, and SF₆+N₂ gas, which is not changed to hydrate, is discharged from the interior of the reactor to the outside. The interior of the reactor containing only hydrate is set at a pressure of 7 bar and a temperature of 293 K, so the hydrate is dissociated. The Quantitative and Qualitative Analysis is performed using GC((Varian CP3800 Gas Chromatograph, TCD) with respect to the dissociated gas. FIGS. 3 and 4 show a result of the above experiment, respectively.

Embodiment 2 Effect Comparison Experiment by Promoter

Pure water(HPLC grade, 99.999%) of 125 ml is injected into a reactor, and the interior of the reactor is purged using SF₆ of 99.99%, and the hydrate formation speed is analyzed by setting a pressure of 7.8 bar and a temperature of 276K. FIG. 5 shows a result of the above experiment.

Embodiment 3 Effect Experiment of LABS Promoter

Aqueous solution including Linear Alkyl Benzene Sulfonate, LABS, Aldrich is prepared depending on concentrations and is substantially mixed and melt in water. 125 ml of LABS aqueous solution prepared by concentrations is injected into the reactor same as the embodiment 2, and the interior of the reactor is purged using SF₆ of 99.9%, and the SF₆ hydrate formation speed is analyzed based on the time by setting a pressure of 7.8 bar and a temperature of 276K. FIG. 5 shows a result of the above experiment.

As shown in FIGS. 3 and 4, as a result of the analysis of gas obtained through a hydrate formation dissociation using SF₆ of 50%(N₂ Balance) gas, a composition of SF₆ is about 80%, and a composition of N₂ is about 20%. Namely, it is known that a separation, purification and recovery of SF₆ and HFCs can be performed through the experiment of the present invention.

As shown in FIG. 5, when SF₆ hydrate is formed with pure water(HPLC grade, 99.999%), even when time is passed, a consumption amount of SF₆, namely, a production amount of SF₆ hydrate is below 0.02 mol, and its formation speed is very slow. When anion such as Linear Alkyl Benzene Sulfonate, LABS, Aldrich is added as a promoter, a consumption amount of SF₆, namely, a production amount of SF₆ hydrate proportionally increases depending on the lapse of time even though there is a certain difference depending on concentrations. Namely, it is possible to form a SF₆ hydrate with a high efficiency and high concentration through an experiment according to the present invention.

As described above, SF₆, HFCs or PFCs are greenhouse gases. Even when 10% of the total emission amount of SF₆ in Korea is separated, purified and recovered, it is possible to advantageously save an environmental cost of above 150 billion won, which leads to great cost saving effects.

The separation, purification and recovery method of SF₆, HFCs or PFCs might be applied for recovering a greenhouse gas for preventing an earth warming phenomenon and separating and recovering SF₆, HFCs or PFCs from other mixed gases.

As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described examples are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims. 

1. A separation, purification and recovery method of fluoro-gas characterized in that a gas hydrate is formed, separated, purified and recovered by reacting a fluoro-gas with water in a gas mixture containing a fluoro-gas.
 2. The method of claim 1, wherein said fluoro-gas is SF₆ (Hexafluorosulfide), HFCs(Hydro fluorocarbons) or PFCs(Perfluorocarbons).
 3. The method of claim 1, wherein said hydrate of fluoro-gas is formed at a temperature of −15° C. through 25° C.
 4. The method of claim 1, wherein said hydrate of a fluoro-gas is formed at a pressure of 1 bar through 25 bar.
 5. The method of claim 1, wherein a promoter is used so as to enhance a hydrate formation speed and separation/purification efficiency.
 6. The method of claim 5, wherein said promoter is formed in a nano-size.
 7. The method of claim 5, wherein said promoter is an anion or cation surface active agent. 